The world virtually revolves around kids on these Web sites

Want green skin and purple hair? No problem — if you're exploring Nickelodeon's recently launched virtual world, Nicktropolis. Prefer to waddle? Try Club Penguin, where you take the form of the flightless bird to decorate igloos and throw snowballs. Like to cuddle? Hug your stuffed Webkinz at night and feed its virtual doppelganger online during the day.

A growing number of Web sites cater to kids as young as 8 with three-dimensional virtual worlds where visitors create avatars (digital characters), furnish their own "rooms," play games and interact in real-time. Players move the avatars by clicking where to go. "We know kids are natural digital multitaskers," said Jason Root, vice president of Nick.com. "We created a digital playground where they're able to do all those things."

On Nickelodeon's TurboNick site, kids can stream videos, but they can't gather with their buddies and talk in real time while watching together, Root said. On Nicktropolis, though, kids can set up these kinds of "virtual play dates," he noted.

Nickelodeon's research found that more than 8 out of 10 kids ages 8 to 14 play games online, and half watch TV shows and videos online. A third exchange instant messages.

Kid-oriented sites are "more evidence that virtual worlds are going to be woven into the fabric of the next generation's lives in a way we probably can't even envision yet," notes blogger Mark Wallace on www.3pointd.com.

Some experts question the benefits of virtual worlds targeted at young children — kids they believe should be out in the real world, using their imaginations, making friends and getting outside.

"A virtual playmate is not nearly as good as a real playmate," said Dr. Michael Rich, director of the Center on Media and Child Health. "I'd hate to see kids rushing home from second grade to meet friends online, as opposed to 'Let's hang out after school and shoot hoops.' "

Virtual kid worlds

Club Penguin: Players choose a penguin and interact with others in the ad-free snowy world, designed for ages 8-14. Participants earn virtual coins by helping others and playing games. Free registration, but players can't decorate penguins or igloos without a $5.95/month membership. Started in October 2005. www.clubpenguin.com

Neopets: A popular virtual community where members and their adopted pets travel around the site to play games, set up shops and chat with other members. According to company estimates, Neopets boasts more than 30 million users; nearly 40 percent of those are age 12 and younger. The site went live in 1999 and is now a subsidiary of MTV Networks. It features banner ads and embedded brand advertising. www.neopets.com

Nicktropolis: Launched last month, the site targets ages 8 to 14 with games, videos, real-time chats and Nickelodeon-themed environments. When avatars enter SpongeBob's Bikini Bottom world, for example, they turn into anchovies. www.nicktropolis.com

Webkinz: Webkinz World began in April 2005. After buying a $8-$10 stuffed animal, owners enter a code and name their new pet. Players can set up houses and earn points to buy food, toys and furniture for their pets. www.webkinz.com.

Whyville: An educationally themed site with 1.7 million registered "citizens." Whyville features its own museum, City Hall and economy. The free site is supported by companies that sponsor themed activities. Launched in 1999, it's geared to upper elementary and middle-school kids, including classrooms. www.whyville.net

Secret code

The real and virtual world blend in Webkinz, described as a cross between Beanie Babies and Neopets. The stuffed animals come with a code that owners enter on the Web site to "adopt" the creatures.

Bellevue mom Robin Gebhart was skeptical when she discovered Webkinz during the holidays. But after checking out the site and deciding it was safe, Gebhart bought several as gifts, including two for her younger children, 9 and 11. She's heard of parents handing them out in place of birthday-party gift bags, so a circle of friends can play online.

Gebhart's 9-year-old is already learning to save and budget points ("KinzCash") for virtual items for her unicorn, Penelope. "I can get them to do all kinds of things, because they want time on Webkinz," said Gebhart, who allots half an hour a day online.

Curious Kidstuff, a West Seattle toy store, has carried Webkinz for about a year. "They're becoming more and more popular," said owner Ann Walker.

From March to December 2006, the number of unique visitors to Webkinz.com jumped nearly 500 percent, from 325,000 to 1.9 million, according to Nielsen/NetRatings.

Geared toward safety

Sites aimed at younger children are less sophisticated than, say, The Sims Online or Teen Second Life, immersive virtual worlds geared to the junior- and high-school crowd. Virtual-world sites differ from massive multiplayer online games (such as RuneScape) in that there is no overarching themed game; the focus is more on socializing. And while they allow chatting among avatars, they are not social-networking sites, à la MySpace.

The kid sites employ extensive safety features, using filters, live monitors and set dialogue (where kids pick phrases to use, rather than composing original messages) to thwart both adult misuse and any sharing of identifying data.

"The point of some of the social-networking sites is putting personal information out there," said Karen Mason, communications director at British Columbia-based Club Penguin. "Everything at Club Penguin is completely the opposite."

At Nicktropolis, "Even if adults come in, there's nothing bad they can do," said Stephen Youngwood, executive vice president of digital media for Nickelodeon and MTVN Kids and Family Group.

Warning: ads ahead

However, "what parents have to realize is the purpose of many of these sites is primarily advertising," said Susan Linn, author of "Consuming Kids." "They're hooking kids on their brands. The sites may protect kids from porn or violence, but they're still designed to manipulate kids into buying."

SpongeBob licensed products, for example, added up to more than $5 billion in retail sales from 2001 to 2006, according to Nickelodeon.

When cartoon characters interact with kids (through a chat bot), "it adds to kids' sense that these characters care about them," said Linn, associate director of the Media Center at the Judge Baker Children's Center in Boston. "Even if they know it's not real, they still respond on a more emotional level."

Club Penguin deliberately eschews advertising, instead relying on $5.95 monthly membership fees. "All of us get bombarded with marketing," Mason said. "It's almost impossible for kids to be online and not see ads. We wanted Club Penguin to be a safe haven.

"The Internet is part of our world, and children are going to use it," she explained. "Club Penguin is a really good training ground, a safe environment to learn some of the basics."

It's up to parents to set limits on kids' online time, Mason said. But the penguin world is so fun, she admits, "it's quite addictive, actually."

Rich, a professor of pediatrics at Harvard Medical School, worries about "immersive" online worlds that are, well, too immersive. "You can get sucked in and spend three or four hours without standing up," he said.

He advocates balance, suggesting kids go online only after they play with friends, eat dinner with their family and do their homework. "This is not the meat and potatoes," Rich said. "This is dessert."

Stephanie Dunnewind: sdunnewind@seattletimes.com or 206-464-2091